Zonal disintegration mechanism of the microcrack-weakened surrounding rock mass in deep circular tunnels

Rock masses without pre-existing macrocracks are considered as granular materials with only microcracks. During excavation of tunnels, microcracks may nucleate, grow and propagate through rock matrix; secondary microcracks may appear, and discontinuous and incompatible deformation of rock masses may occur. The classical continuum elastoplastic theory is not suitable for analyzing discontinuous and incompatible deformation of rock masses any more. In this paper, a new non-Euclidean model is established to investigate zonal disintegration mechanism of the surrounding rock masses around a deep circular tunnel. Effect of damage variable on the zonal disintegration under non-hydrostatic stress condition is taken into account. Based on non-Euclidean model of the discontinuous and incompatible deformation of rock mass, the effect of the half length and density of microcracks on distribution of stresses in the surrounding rock masses around a deep circular tunnel is investigated. The stress concentration at the tips of microcracks located in vicinity of stress wave crest is comparatively large, which may lead to the unstable growth and coalescence of secondary microcracks, and consequently the occurrence of fractured zones. On the other hand, the stress concentration at the tips of microcracks located around stress wave trough is relatively small, which may lead to arrest of microcracks, and thus the non-fractured zones. The alternative appearance of stress wave crest and stress trough thus may induce the alternative occurrence of fractured and non-fractured zones in deep rock masses.